NZ616061B

NZ616061B - Recycling toxic gases

Info

Publication number: NZ616061B
Application number: NZ616061A
Authority: NZ
Inventors: Lance Allen Dear; Richard John Newson
Original assignee: Lance Allen Dear; Richard John Newson
Filing date: 2013-09-27
Publication date: 2014-03-21

Abstract

616061 Disclosed herein is a method of obtaining fumigant for re-use or disposal, comprising the steps of passing a gaseous flow comprising used fumigant such as methyl bromide through a container which contains fumigant absorbent, such as activated carbon; heating the absorbent so that it releases at least some of the absorbed fumigant to a gaseous flow; capturing the released fumigant by cooling to -5°C to 25°C and to have a pressure of 1 bar to 15 bar; and subsequently at a temperature of -5°C to -45°C and to have a pressure of 15 to 45 bar. Additionally disclosed is an apparatus for obtaining fumigant for re-use. at least some of the absorbed fumigant to a gaseous flow; capturing the released fumigant by cooling to -5°C to 25°C and to have a pressure of 1 bar to 15 bar; and subsequently at a temperature of -5°C to -45°C and to have a pressure of 15 to 45 bar. Additionally disclosed is an apparatus for obtaining fumigant for re-use.

Description

COMPLETE SPECIFICATION TITLE Recycling toxic gases FIELD OF INVENTION This invention relates to the recycling of toxic gases, for example the type used to fumigate logs at a wharf or for export or import generally.

BACKGROUND The release of certain fumigants to the atmosphere after a fumigation process presents health and environmental risks. It is known to capture used fumigant from an air stream by forcing it through a canister loaded with activated carbon. As this occurs the fumigant is absorbed by the carbon. However after a period of use the carbon becomes saturated and loses its ability to absorb any further. In some cases the spent carbon is then disposed of by burying it in the ground. This, however, is not an environmentally friendly solution. It is an object of a preferred embodiment of the invention to facilitate the capture of used fumigant, preferably for re-use.

SUMMARY OF THE INVENTION According to one aspect of the invention there is provided a method of obtaining fumigant for re-use or disposal, comprising the steps of: a) passing a gaseous flow (eg an airflow) comprising used fumigant (eg methyl bromide) through a container which contains fumigant absorbent (eg activated carbon) so that the fumigant is at least partially absorbed by the absorbent; b) causing the absorbent to be heated so that it releases at least some of the absorbed fumigant to a gaseous flow (eg an airflow); c) capturing the released fumigant and causing it to be cooled to -5°C to 25°C (preferably 0°C to 20°C) and to have a pressure of 1 bar to 15 bar (preferably 5 bar to 10 bar); and d) receiving the fumigant from step c) and causing it to have a temperature of -5°C to -45°C (preferably -15°C to -30°C) and to have a pressure of 15 to 45 bar (preferably 15 bar to 25 bar).

Preferably the fumigant is methyl bromide.

Preferably the fumigant is compressed and cooled in stages using: i) a first chamber where the fumigant is caused to have a temperature of approximately 30 to 60 °C and a pressure of 2 to 5 bar; ii) a second chamber where the fumigant is caused to have a temperature of 0 to -10°C and a pressure of 7 to 12 bar; and iii) a third chamber where the fumigant is caused to have a temperature of -15 to -30°C and a pressure of 15-25 bar.

Preferably water is removed from the fumigant during cooling and compression of the fumigant.

Preferably the fumigant from step d) is re-used.

Preferably the gaseous flow mentioned at step a) has been compressed to remove water before being passed through the container which contains absorbent.

According to a further aspect of the invention there is provided apparatus obtaining fumigant for re-use, comprising: a) means adapted for passing a gaseous flow (eg an airflow) of used fumigant (eg methyl bromide) through a container which contains fumigant absorbent (eg activated carbon) so that the fumigant is at least partially absorbed by the absorbent; b) means adapted to cause the absorbent to be heated so that it releases at least some of the absorbed fumigant to a gaseous flow (eg an airflow); c) means adapted to receive the released fumigant and cause it to be cooled to -5°C to 25°C (preferably 0°C to 20°C) and to have a pressure of 1 bar to bar (preferably 5 bar to 10 bar); and d) means adapted to receive the fumigant mentioned at c) and cause it to have a temperature of -5°C to -45°C (preferably -15°C to -30°C) and to have a pressure of 15 to 45 bar (preferably 15 bar to 25 bar).

Preferably the apparatus is adapted for effective use when the fumigant is methyl bromide.

Preferably the apparatus has means adapted to cool and compress the fumigant in stages using: i) a first chamber adapted to cause the fumigant to have a temperature of approximately 30 to 60 °C and a pressure of 2 to 5 bar; ii) a second chamber adapted to cause the fumigant to have a temperature of 0 to -10°C and a pressure of 7 to 12 bar; and iii) a third chamber adapted to cause the fumigant to have a temperature of -15 to -30°C and a pressure of 15-25 bar.

Preferably the apparatus has means adapted to remove water from the fumigant during cooling and compression of the fumigant.

Preferably the apparatus has means to compress the gaseous flow mentioned at item a) to remove water before being passed through the container which contains absorbent.

BRIEF DESCRIPTION OF THE DRAWING Some preferred forms of the invention will now be described by way of example and with reference to the accompanying drawing, of which: Figure 1 is a schematic illustration of a method and apparatus for obtaining fumigant for re-use.

DETAILED DESCRIPTION Logs which need to be fumigated, for example before or after being imported or exported, are subjected to gaseous methyl bromide dispersed in an air stream. After the fumigation process it is not desirable, for safety and environmental reasons, to vent the methyl bromide laden air to the atmosphere. To remove the used methyl bromide from the airflow it is pumped through one or more portable cylinders containing activated carbon. The cylinders have inlet and outlet ports to facilitate this. The carbon absorbs the methyl bromide. Preferably the airflow carrying the fumigant is compressed to remove water from it prior to contact with the carbon. After extended or repeated periods of use the carbon becomes saturated and unable to absorb any further methyl bromide. The cylinders are then taken away for processing.

Referring to figure 1, to remove the methyl bromide the cylinders 1 are placed in a chamber 2, and their outside surfaces are subjected to hot air at about 100°C to about 175 C by way of a closed loop heat source 3. Hot air exceeding 100°C, and preferably exceeding 120°C, and most preferably exceeding 125°C, from a heat exchanger 4 is simultaneously pumped in a loop fashion through the cylinders 1. This is facilitated by the inlet and outlet ports of each cylinder. The effect of heat on the outsides and insides of the cylinders 1 causes the methyl bromide to be heated to approximately 100°C to 175 C (preferably at least 120°C) to be released from the carbon and then carried out of the cylinders 1 in the air stream. During this process the return airflow from the cylinders and the temperature of the carbon is monitored and recorded electronically, and adjusted if need be. The carbon is preferably exposed to heat until it has released at least approximately 75% to 95% of the absorbed methyl bromide. In alternative embodiments the carbon may be heated by only the air passing through the cylinders 1, that is without applying heat to the outside of the cylinders.

The methyl bromide laden air (which has a water component) is pumped or diverted in a controlled release manner to a first stage cooling and compression chamber 5 to be cooled and compressed to a temperature of approximately 30 to 60 °C and a pressure of 2 to 5 bar. From there the methyl bromide is caused to move in a controlled release manner to a second stage cooling and compression chamber 6 where it is cooled and compressed to a temperature of 0 to -10°C and a pressure of 7 to 12 bar. The methyl bromide it is subsequently caused to move in a controlled release manner to a third stage cooling and compression chamber 7 where it is cooled and compressed to a temperature of -15 to -30°C and a pressure of 15-25 bar. At each cooling and compression stage water is removed so that the methyl bromide becomes progressively purer. The cooled and compressed methyl bromide is finally pumped to a holding chamber 8 from which it can be drawn or packaged and re-used.

While the method and apparatus has been described with three progressive compression and cooling steps it can be adjusted to have fewer or more of these depending on operational requirements and parameters. In some cases there may be one or more cooling only step, and in some cases there may be one or more compression only step. The invention can also be used with fumigants other than methyl bromide and in such cases the temperature and pressure levels may be adjusted appropriately.

While some preferred forms of the invention have been described by way of example, it should be appreciated that modifications and improvements can occur without departing from the scope of the following claims.

WHAT WE

Claims

CLAIM IS

1. A method of obtaining fumigant for re-use or disposal, comprising the steps of: a) passing a gaseous flow comprising used fumigant through a container 5 which contains fumigant absorbent so that the fumigant is at least partially absorbed by the absorbent; b) causing the absorbent to be heated so that it releases at least some of the absorbed fumigant to a gaseous flow; c) capturing the released fumigant and causing it to be cooled to -5°C to 10 25°C and to have a pressure of 1 bar to 15 bar; and d) receiving the fumigant from step c) and causing it to have a temperature of -5°C to -45°C and to have a pressure of 15 to 45 bar.

2. A method according to claim 1, wherein the gaseous flow in each case comprises 15 an airflow.

3. A method according to claim 1 or 2, wherein the fumigant comprises methyl bromide.

4. A method according to claim 1, 2 or 3, wherein the absorbent comprises activated carbon.

5. A method according to and one of the preceding claims, wherein step c) comprises 25 capturing the released fumigant and causing it to be cooled to 0°C to 20°C and to have a pressure of 5 bar to 10 bar.

6. A method according to and one of the preceding claims, wherein step (d) comprises receiving the fumigant from step (c) and causing it to have a 30 temperature of -15°C to -30°C and to have a pressure of 15 bar to 25 bar.

7. A method according to and one of the preceding claims, wherein the fumigant is compressed and cooled in stages using: i) a first chamber where the fumigant is caused to have a temperature of 35 approximately 30 to 60 °C and a pressure of 2 to 5 bar; ii) a second chamber where the fumigant is caused to have a temperature of 0 to -10°C and a pressure of 7 to 12 bar; and iii) a third chamber where the fumigant is caused to have a temperature of -15 to -30°C and a pressure of 15-25 bar.

8. A method according to any one of the preceding claims, wherein water is removed from the fumigant during cooling and compression of the fumigant.

9. A method according to any one of the preceding claims, wherein the gaseous flow 10 mentioned at step a) has been compressed to remove water before being passed through the container which contains absorbent.

10. A method according to any one of the preceding claims, wherein the fumigant from step d) is re-used.

11. Apparatus obtaining fumigant for re-use, comprising: a) means adapted for passing a gaseous flow of used fumigant through a container which contains fumigant absorbent so that the fumigant is at least partially absorbed by the absorbent; 20 b) means adapted to cause the absorbent to be heated so that it releases at least some of the absorbed fumigant to a gaseous flow; c) means adapted to receive the released fumigant and cause it to be cooled to -5°C to 25°C and to have a pressure of 1 bar to 15 bar; and d) means adapted to receive the fumigant mentioned at c) and cause it to 25 be cooled to -5°C to -45°C and to have a pressure of 15 to 45 bar.

12. Apparatus according to claim 11, wherein the means at item a) is adapted for passing an airflow of used methyl bromide through the container. 30

13. Apparatus according to claim 11 or 12, wherein the means at item b) is adapted to cause the fumigant to be released to an airflow.

14. Apparatus according to claim 11, 12 or 13, adapted for use when the absorbent comprises activated carbon.

15. Apparatus according to any one of claims 11 to 14, wherein at the means at item c) is adapted to receive the released fumigant and cause it to have a temperature of 0°C to 20°C and to have a pressure of 5 bar to 10 bar.

16. Apparatus according to any one of claims 11 to 15, wherein the means at item d) is adapted to receive the fumigant mentioned at c) and cause it to have a temperature of -15°C to -30°C and to have a pressure of 15 bar to 25 bar. 10

17. Apparatus according to any one of claims 11 to 16, adapted to cool and compress the fumigant in stages using: a) a first chamber adapted to cause the fumigant to have a temperature of approximately 30 to 60 °C and a pressure of 2 to 5 bar; b) a second chamber adapted to cause the fumigant to have a temperature 15 of 0 to -10°C and a pressure of 7 to 12 bar; and c) a third chamber adapted to cause the fumigant to have a temperature of -15 to -30°C and a pressure of 15-25 bar.

18. Apparatus according to any one claims 11 to 16, having means adapted for 20 removing water from the fumigant during cooling and compression of the fumigant.

19. Apparatus according to any one of claims 11 to 18, having means to compress the gaseous flow mentioned at item a) to remove water before being passed through the container which contains absorbent.

20. A method according to claim 1, substantially as herein described.

21. Apparatus according to claim 11, substantially as herein described.